Onto.PT: Towards the Automatic Construction of a Lexical Ontology ...

2.2. Lexical Knowledge Formalisms and Resources 15
contains(bottle, wine)
is-a(wine, beverage)
Figure 2.2: Meaning representation 1: logical predicates.
Figure 2.3: Meaning representation 2: directed graph.
wine
is-a: beverage
container: bottle
Figure 2.4: Meaning representation 3: semantic frame.
these abstractions may be used together with computational applications that, in
order to achieve their goal, need to access lexical-semantic knowledge.
2.2.2 Thesauri
A thesaurus is a resource structured on the synonymy relation, as it groups lexical
items together with their synonyms (or, according to the point of view, near
synonyms (Edmonds and Hirst, 2002)). As a lexical item may have more than one
meaning, it can be included in more than one group. Each inclusion of a lexical
item in a group may thus be seen as a word sense, which means that ambiguous
words will be included in more than one group. Moreover, a group of lexical items
may be seen as the possible lexicalisations of a natural language concept.
Roget’s Thesaurus (Roget, 1852), whose first edition is more than 150 years old,
is the first ever and a widely-used English thesaurus. For Portuguese, TeP (Dias-
Da-Silva and de Moraes, 2003; Maziero et al., 2008) is an electronic thesaurus for
the Brazilian variant, created manually. In order to illustrate how the entries of a
thesaurus may look like, figure 2.5 shows some of the entries for the word thesaurus
in the online service Thesaurus.com 6 . Figure 2.6 shows the entries for the word
canto in TeP. This word can either refer to a corner, or to a song.
Even though a thesaurus might represent other semantic relations besides synonymy,
in the context of this thesis, the term thesaurus will be used to describe a
resource that simply groups synonymous lexical items.
2.2.3 Lexical Networks
Lexical networks are graph structures, N = (V, E), with |V | nodes and |E| edges,
E ⊂ V 2 , where each node wi ∈ V represents a lexical item and each edge between
6 Available online from http://thesaurus.reference.com (August 2012)